Mold for use in a gas-assisted injection molding system and ejector pin subsystem including a blocking pin assembly for use therein

ABSTRACT

A mold for use in a gas-assisted injection molding system includes an ejector pin subsystem including a blocking pin assembly which not only blocks the flow of molten plastic through a secondary runner but also helps to eject solid plastic from the mold. The mold also includes an adjustable overflow pin assembly and a conically-shaped spill cavity flow-coupled by the secondary runner to an article-defining cavity of the mold. The blocking pin assembly together with the adjustable overflow pin assembly are mounted on an ejector plate to move therewith between extended and retracted positions of the ejector plate. The blocking pin assembly includes a blocking pin which is slidably fit within a mold half to move between an extended blocking position to block the flow of molten plastic through the secondary runner and a retracted position to allow the flow of molten plastic through the secondary runner and into the spill cavity. The blocking pin assembly includes a hydraulic cylinder for slidably mounting and moving the blocking pin relative to the ejector plate. The blocking pin has an end surface which partially defines the secondary runner in its retracted position and partially defines the article-defining cavity in its extended blocking position. The adjustable overflow pin assembly and the blocking pin assembly, as well as the other ejector pins mounted on the ejector plate, eject plastic from the article-defining cavity, the spill cavity, and the secondary runner in the extended position of the ejector plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent applications entitled "MoldFor Use In A Gas-Assisted Injection Molding System And Gas Pin AssemblyFor Use Therein" filed Sep. 22, 1997 and having U.S. Ser. No.08/935,013; "Mold For Use In A Gas-Assisted Injection Molding System AndAdjustable Overflow Pin Assembly Use Therein" now U.S. Pat. No.5,869,105 "Mold For Use In A Gas-Assisted Injection Molding System AndEjector Pin Subsystem Including A Split Pin For Use Therein" filed onApr. 14, 1998 and having U.S. Ser. No. 09/059,947; and "Mold For Use InA Plastic Injection Molding system And Venting Pin Assembly For UseTherein" filed on Mar. 12, 1998 and having U.S. Ser. No. 09/041,333.

TECHNICAL FIELD

This invention relates to molds and ejector pin subsystems for usetherein and, in particular, to molds for use in gas-assisted injectionmolding systems and ejector pin subsystems including blocking pinassemblies for use therein.

BACKGROUND ART

U.S. Pat. No. 5,098,637 discloses a method and system for injectionmolding hollow plastic articles with pressurized gas which provides fordisplacement by the gas of a portion of plastic from the mold cavityinto a flow-coupled spill cavity. The volume of the spill cavity may bevaried to control the quantity of displaced plastic such as by a leadscrew.

U.S. Pat. No. 5,607,640 (i.e. '640 patent) discloses in FIGS. 1-4thereof, the use of a spill cavity with a blocking pin and shims tocontrol the volume of plastic going into the spill cavity. The pin is inits up position to block plastic flow from the article-defining cavity,through a runner and into the spill cavity. Subsequently, the pin movesto its down position to allow plastic to go to the spill cavity bypressurized gas. In the remainder of the '640 patent, a method andsystem are disclosed where the volume of the spill cavity is allowed toincrease in a controlled fashion to a final volume based on the amountof plastic injected into the mold cavity. The volume of the spill cavityincreases during a step of displacing the plastic into the spill cavity.In this way, the method and system eliminate the need for a shut-off orblocking pin. In two disclosed embodiments, pistons are utilized topurge or displace plastic from the spill cavity.

European Patent Document No. 393,315 discloses a spill subgate with ablocking hydraulic pin.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a mold for use in agas-assisted injection molding system and ejector pin subsystem for usetherein wherein the subsystem includes an ejector plate and a blockingpin assembly mounted on the ejector plate to move therewith and whereinthe assembly includes a blocking pin slidably fit within the mold to notonly block the flow of molten plastic within a secondary runner in themold but also to cooperate with the rest of the subsystem to ejectsolidified plastic from an article-defining cavity, a spill cavity andthe secondary runner. This is a practical design which is not onlyrelatively inexpensive but also is simple in operation and forservicing.

In carrying out the above object and other objects of the presentinvention, a mold for use in a gas-assisted injection molding system isprovided. The mold includes a first mold half and a second mold half.The first and second mold halves are movable relative to each otherbetween an open position and a closed position. The first and secondmold halves define an article-defining cavity, a spill cavity, and asecondary runner for flow coupling the spill cavity to thearticle-defining cavity. The mold also includes an ejector pin subsystemincluding an ejector plate supported to move relative to the second moldhalf between extended and retracted positions and a blocking pinassembly mounted on the ejector plate to move therewith. The blockingpin assembly includes a blocking pin slidably fit within the second moldhalf to move relative to the ejector plate between an extended blockingposition to block the flow of molten plastic through the secondaryrunner and a retracted position to allow the flow of molten plasticthrough the secondary runner and into the spill cavity. The ejector pinsubsystem also includes at least one ejector pin also mounted on theejector plate and slidably fit within the second mold half to move withthe ejector plate relative to the second mold half in an open positionof the mold. The at least one ejector pin and the blocking pin ejectplastic from the article-defining cavity, the spill cavity, and thesecondary runner in the extended position of the ejector plate.

Preferably, the blocking pin assembly includes a cylinder for slidablymounting and moving the blocking pin relative to the ejector plate.Preferably, the cylinder is a hydraulic cylinder.

Also, preferably, the blocking pin has an end surface which partiallydefines the secondary runner in its retracted position and partiallydefines the article-defining cavity in its extended blocking position.

Also, preferably, the at least one ejector pin moves within the spillcavity to eject plastic from the spill cavity and the secondary runnerin the extended position of the ejector plate.

Still, preferably, the molten plastic flows in a first direction throughthe secondary runner to reach the spill cavity and wherein the blockingpin moves in the secondary runner in a second direction substantiallyopposite the first direction during movement of the blocking pin fromits retracted position to its extended blocking position.

Still further in carrying out the above object and other objects of thepresent invention, in a mold having a first mold half and a second moldhalf wherein the first and second mold halves move relative to eachother between an open position and a closed position and wherein thefirst and second mold halves defined an article-defining cavity, a spillcavity, and a secondary runner for flow coupling the spill cavity to thearticle-defining cavity, an ejector pin subsystem is provided. Theejector pin subsystem includes an ejector plate supported to moverelative to the second mold half between extended and retractedpositions thereof. The ejector pin subsystem also includes a blockingpin assembly mounted on the ejector plate to move therewith. Theblocking pin assembly includes a blocking pin slidably fit within thesecond mold half to move relative to the ejector plate between anextended blocking position to block the flow of molten plastic throughthe secondary runner and a retracted position to allow the flow ofmolten plastic through the secondary runner and into the spill cavity.The ejector pin subsystem further includes at least one ejector pin alsomounted on the ejector plate to move therewith and slidably fit withinthe second mold half to move with the ejector plate relative to thesecond mold half in the open position of the mold. The at least oneejector pin and the blocking pin eject plastic from the article-definingcavity, the spill cavity, and the secondary runner in the extendedposition of the ejector plate.

The above objects and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view, partially broken away and in cross-section, of a moldand an ejector pin subsystem both of which are constructed in accordancewith the present invention; and

FIG. 2 is a block diagram flow chart illustrating the various stepsutilized in a gas-assisted injection molding system which utilizes themold and ejector pin subsystem of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawing Figures, there is illustrated in FIG. 1 amold, generally indicated at 10, for use in a gas-assisted injectionmolding system. The mold 10 includes a first mold half 12 and a secondmold half 14. The first and second mold halves 12 and 14, respectively,are movable relative to each other between an open position and a closedposition as shown in FIG. 1, wherein the first and second mold halves 12and 14 respectively define an article-defining cavity 16.

The second mold half 14 includes a gas passageway 18 which extends froman exterior surface (not shown) of the second mold half 14 to an innerinterior surface 20 of the second mold half 14 in fluid communicationwith the article-defining cavity 16.

The second or stationary mold half 14 includes a sprue 22 forcommunicating thermoplastic material to a runner 24 which, in turn,communicates with the article-defining cavity 16 via a gate 26. Athermoplastic flow path is defined by the sprue 22, the runner 24 andthe gate 26. Ejector pins 28 extend through the first or movable moldhalf 12 and are connected to an ejector plate 29. The ejector plate 29is supported to move relative to the first mold half 12 from a retractedposition to an extended position to eject a completed part from thearticle-defining cavity 16 as well as the plastic in the runner 24 andthe sprue 22.

The mold 10 also includes a gas pin assembly, generally indicated at 30.The gas pin assembly 30 includes a one-piece housing 32. A base portionof the housing 32 is threadedly secured to the second mold half 14 atthe interior surface 20 of the second mold half 14 so that the gas pinassembly 30 can be readily removed from the second mold half 14 in theopen position of the mold 10. A rubber O-ring is typically providedabout the base portion of the housing 32 to seal the housing 32 withinthe second mold half 14.

Preferably, the housing 32 also includes a hexagonal head portion sothat the assembly 30 can be readily removed from the second mold half 14in the open position of the mold 10 by a conventional tool (not shown).

The housing 32 includes an elongated aperture formed therein incommunication with and aligned with the gas passageway 18 to permit theflow of gas therethrough.

The base portion of the housing 32 is also internally threaded tothreadedly secure therein a holding device in the form of a set screw 42which has a gas hole formed completely therethrough to permit the flowof gas therethrough.

The gas pin assembly 30 also includes a porous insert 48 comprising asintered material such as aluminum, copper, nickel, steel, bronze,porcelain, and brass which permits the flow of gas therethrough butprevents the passage of molten plastic therethrough. The insert 48 isheld in position within the aperture by the set screw 42 at one endthereof and by flanges of the head portion at the opposite end thereof.

The sintered material is preferably a bronze sintered material and canfilter out foreign particles down to 20 microns. However, the micronsize can be varied depending on the type of plastic utilized in themolding process.

Further details of the gas pin assembly 30 can be found within theabove-noted patent application entitled "Mold For Use In A Gas-AssistedInjection Molding System And Gas Pin Assembly For Use Therein". Whilethe gas pin assembly 30 is illustrated as the particular mechanism forinjecting pressurized gas into the article-defining cavity 16, othermechanism can be utilized to inject pressurized gas into thearticle-defining cavity 16 as illustrated and described in the prior artpatents noted in the "Background Art" portion of this application.

The mold 10 also includes a conically-shaped spill cavity 50 and asecondary runner, generally indicated at 52, for flow coupling the spillcavity 50 to the article-defining cavity 16. The secondary runner 52includes a vertically extending portion 53, an angled portion 54 and ahorizontally-extending portion 56 through which molten plastic flowsfrom the article-defining cavity 16 to the conically-shaped spill cavity50 upon the injection of pressurized gas into the article-definingcavity 16.

The mold 10 of the present invention also includes an adjustableoverflow pin assembly, generally indicated at 58. The pin assembly 58includes a pin 60 slidably fit within the mold half 12 and connected tothe ejector plate 29 to move relative to the mold half 12 in an openposition of the mold 10 upon movement of the ejector plate 29 relativeto the mold half 12 between extended and retracted positions thereof.

The pin assembly 58 also includes a conical stack of annular shims 62which are removably secured to the ejector pin 60 by means of a threadedfastener such as a screw, generally indicated at 64, which extendsthrough the shims 62 and into an internally threaded hole 66 formed inan end face or surface 68 of the ejector pin 60. The screw 64 has a headportion 65 which is in abutting engagement with the uppermost shim 62.The top surface of the head portion 65 is flush with the top surface ofthis shim 62.

The shims 62 move with the ejector pin 60 within the conically-shapedspill cavity 50 during movement of the ejector plate 29 from itsretracted position to its extended position so that the assembly 58ejects plastic from the spill cavity 50. The conical stack of shims 62has an outer surface taper approximately in the range of 2° to 8° and ispreferably approximately 5°. In this way, the shims 62 form a tight fitwith the spill cavity 50 which has a corresponding taper to its interiorsurface. The annular shims 62 form the tight fit within the spill cavity50 in the retracted position of the ejector plate 29.

Two or more annular shims 62 define the stack of annular shims 62. Thenumber of annular shims 62 is dependent upon how much molten plasticneed be removed from the article-defining cavity 16 to define thedesired hollow plastic part formed within the article-defining cavity16.

The mold 10 also includes a blocking pin assembly, generally indicatedat 70, also mounted on the ejector plate 29 to move therewith. Theblocking pin assembly 70 includes a blocking pin 72 which is alsoslidably fit within the mold half 12 to move relative to the ejectorplate 29 to an extended plastic blocking position within the verticallyextending portion 53 of the secondary runner 52 to block the flow ofmolten plastic through the secondary runner 52 as shown in FIG. 1.

The pin 72 is retractable within the portion 53 of the secondary runner52 to a retracted position by a hydraulic cylinder 76 which is alsomounted on the ejector plate 29 to move therewith. In the retractedposition of the blocking pin 72 within the portion 53 of the secondaryrunner 52, molten plastic is allowed to flow from the article-definingcavity 16 into the secondary runner 52 and then into thearticle-defining cavity 50. The blocking pin 72 has an end surface orface 78 which partially defines the runner 52 in the retracted positionof the blocking pin 72 and which partially defines the article-definingcavity 16 in the extended position of the blocking pin 72.

Referring now to FIG. 2, there is illustrated in block diagram flowchart form various process steps implemented by a gas-assisted injectedmolding system including the mold 10 of the present invention.

At block 80, an injection molding cycle begins wherein the mold 10 isclosed and the hydraulic or blocking pin 72 is extended within thevertically extending portion 53 of the secondary runner 52 to block thesecondary runner 52 as illustrated in FIG. 1.

At block 82, the article-defining cavity 16 is substantially filled withplastic.

At block 84, pressurized gas is injected into the article-definingcavity 16 and the hydraulic pin 72 is retracted substantiallysimultaneously with the injection of pressurized gas.

At block 86, excess plastic displaced by the pressurized gas within thearticle-defining cavity 16 travels through the secondary runner 52 andinto the adjustable overflow or spill cavity 50.

At block 88, the molten plastic within the article-defining cavity 16,within the secondary runner 52 and within the spill cavity 50 is allowedto cool and the pressurized gas is exhausted from the article-definingcavity 16.

At block 90, the mold 10 is opened.

At block 92, the ejector plate 29 which carries the hydraulic cylinder76, the ejector pin 60, and the other ejector pins 28 is extended towardthe mold half 14 and the pins 72 and 28 and the shims 62 eject plasticfrom the sprue 22 and runner 24, the plastic article from thearticle-defining cavity 16, plastic from the secondary runner 52, andplastic from the overflow or spill cavity 50.

At block 94, the ejector plate 29 is retracted by moving it relative tothe mold half 12 to the position shown in FIG. 1.

At block 96, the mold 10 is closed and the pin 72 is extended to blockthe portion 53 of the secondary runner 52 to await the beginning ofanother injection molding cycle.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

What is claimed is:
 1. A mold for use in a gas-assisted injectionmolding system, the mold comprising:a first mold half; a second moldhalf, the first and second mold halves being movable relative to eachother between an open position and a closed position, wherein the firstand second mold halves define an article-defining cavity, a spillcavity, and a secondary runner for flow coupling the spill cavity to thearticle-defining cavity; and an ejector pin subsystem including:anejector plate supported to move relative to the second mold half betweenextended and retracted positions; a blocking pin assembly mounted on theejector plate to move therewith, the blocking pin assembly including ablocking pin slidably fit within the second mold half to move relativeto the ejector plate between an extended blocking position to block theflow of molten plastic through the secondary runner and a retractedposition to allow the flow of molten plastic through the secondaryrunner and into the spill cavity; and at least one ejector pin alsomounted on the ejector plate and slidably fit within the second moldhalf to move with the ejector plate relative to the second mold half inthe open position of the mold, the at least one ejector pin and theblocking pin ejecting plastic from the article-defining cavity, thespill cavity, and the secondary runner in the extended position of theejector plate.
 2. The mold as claimed in claim 1 wherein the blockingpin assembly includes a cylinder for slidably mounting and moving theblocking pin relative to the ejector plate.
 3. The mold as claimed inclaim 2 wherein the cylinder is a hydraulic cylinder.
 4. The mold asclaimed in claim 1 wherein the blocking pin has an end surface andwherein the end surface partially defines the secondary runner in itsretracted position and partially defines the article-defining cavity inits extended blocking position in the closed position of the mold. 5.The mold as claimed in claim 1 wherein the at least one ejector pinmoves within the spill cavity to eject plastic from the spill cavity andthe secondary runner in the extended position of the ejector plate. 6.The mold as claimed in claim 1 wherein the molten plastic flows in afirst direction through the secondary runner to reach the spill cavityand wherein the blocking pin moves in the secondary runner in a seconddirection substantially opposite the first direction during movement ofthe blocking pin from its retracted position to its extended blockingposition.
 7. In a mold having a first mold half and a second mold half,the first and second mold halves being movable relative to each otherbetween an open position and a closed position and wherein the first andsecond mold halves define an article-defining cavity, a spill cavity,and a secondary runner for flow coupling the spill cavity to thearticle-defining cavity, an ejector pin subsystem comprising:an ejectorplate supported to move relative to the second mold half betweenextended and retracted positions; a blocking pin assembly mounted on theejector plate to move therewith, the blocking pin assembly including ablocking pin slidably fit within the second mold half to move relativeto the ejector plate between an extended blocking position to block theflow of molten plastic through the secondary runner and a retractedposition to allow the flow of molten plastic through the secondaryrunner and into the spill cavity; and at least one ejector pin alsomounted on the ejector plate and slidably fit within the second moldhalf to move with the ejector plate relative to the second mold half inthe open position of the mold, the at least one ejector pin and theblocking pin ejecting plastic from the article-defining cavity, thespill cavity, and the secondary runner in the extended position of theejector plate.
 8. The ejector pin subsystem of claim 7 wherein theblocking pin assembly includes a cylinder for slidably mounting andmoving the blocking pin relative to the ejector plate.
 9. The ejectorpin subsystem of claim 8 wherein the cylinder is a hydraulic cylinder.10. The ejector pin subsystem of claim 7 wherein the blocking pin has anend surface and wherein the end surface partially defines the secondaryrunner in its retracted position and partially define thearticle-defining cavity in its extended blocking position in the closedposition of the mold.
 11. The ejector pin subsystem of claim 7 whereinthe at least one ejector pin moves within the spill cavity to ejectplastic from the spill cavity and the secondary runner in the extendedposition of the ejector plate.
 12. The ejector pin subsystem of claim 7wherein the molten plastic flows in a first direction through thesecondary runner to reach the spill cavity and wherein the blocking pinmoves in the secondary runner in a second direction substantiallyopposite the first direction during movement of the blocking pin fromits retracted position to its extended blocking position.